Pneumatic shock testing machine

ABSTRACT

The machine has a baseplate, a vertically extending cylinder thereon supporting a loading stage with access door and a vertically extending guide tube secured thereon aligned with the cylinder. A tubular seismic mass is slidable upward by means of air pressure in the cylinder and as a tubular stop therewithin, secured at its lower end in the lower portion of the cylinder. The stop has its upper end in sealed engagement with the passage through the mass, the stop tube being adapted to supply air to the mass passage above the seal. An annular anvil, guided in and supported by the mass, and carrying an annular shock pad thereon, is capable of movement upward beyond the mass when pressure is supplied through the stop tube, the pad then making sealed contact with the lower end of the guide tube, the passage through anvil and pad being capable of delivering air under a cylindrical specimen-carrying carriage carried on the pad for forcing the carriage upward in the guide tube. Latch means secured on the guide tube is operable to detain the carriage in raised position when air from the stop tube is shut off and the anvil and pad are lowered on the mass. The guide tube has vent means and air pressure supply means for firing the carriage downward when the vent is closed and the latch is released, the carriage striking the pad supported on the raised mass. Programming means, operating valves for supplying and venting air under the mass, supplying air through the stop tube, and for supplying air pressure and venting the guide tube above the latch and for operating the latch, may be set for raising the mass and the carriage, firing the carriage downward one or more times and then lowering the mass so that the carriage may be removed through the access door.

United States Patent [72] Inventors Gllhert F. Hill Skaneateles; Frederick J. Loetterle, Marietta; Farris Smith, Skaneatdes; Stanley Gray,

Sltaneateles, all 0!, RM.

[2]] Appl. No. 883,427

[22] Filed Dec.9, 1969 [45] Patented Aug. 24, 1971 [73] Assignee Mechanical Technology laeorponhd Latham, N.Y.

[$4] PNEUMATIC SHOCK TESTING MACHINE 4 Claims, 8 Drawlng Figs.

[52] U.S.Cl...,.v 73/12, 73/82 5| lnt.Cl Goln 3/08 [50] Field olSearch 73/l2;8/7, 8; 72/453 [56] References Cited UNITED STATES PATENTS Rev 26,279 10/1967 Boynton 73/12 334,475 1/1886 Shaw 89/8 2,604,777 7/1952 Armstrongetal. 73/12 2,810,288 10/1957 llerron etal 73/12 3,062,036 11/1962 York 73/12 3,079,786 3/1963 Fowler et al.. 73/12 3,148,530 9/1964 Woods 73/12 3,209,580 10/1965 Colby 73/12 3,360,979 1/1968 Jensen et a1. 73/12 OTHER REFERENCES Compressed Gas Gun" Review of Scientific Instruments Vol. 35 #1. 1/64 pp. 1 l-l4by S. Thunborget a1.

Primary ExaminerRichard C. Queisser Assistant Examiner-John Whalen AtrorneyBruns & Jenney ABSTRACT: The machine has a baseplate, a vertically ex tending cylinder thereon supporting a loading stage with access door and a vertically extending guide tube secured thereon aligned with the cylinder. A tubular seismic mass is slidable upward by means of air pressure in the cylinder and as a tubular stop therewithin, secured at its lower end in the lower portion of the cylinder. The stop has its upper end in sealed engagement with the passage through the mass, the stop tube being adapted to supply air to the mass passage above the seal. An annular anvil, guided in and supported by the mass, and carrying an annular shock pad thereon, is capa' ble of movement upward beyond the mass when pressure is supplied through the stop tube, the pad then making sealed contact with the lower end of the guide tube, the passage through anvil and pad being capable of delivering air under a cylindrical specimen-carrying carriage carried on the pad for forcing the carriage upward in the guide tube. Latch means secured on the guide tube is operable to detain the carriage in raised position when air from the stop tube is shut 0H and the anvil and pad are lowered on the mass. The guide tube has vent means and air pressure supply means for firing the carriage downward when the vent is closed and the latch is released, the carriage striking the pad supported on the raised mass. Programming means, operating valves for supplying and venting air under the mass, supplying air through the stop tube, and for supplying air pressure and venting the guide tube above the latch and for operating the latch, may be set for raising the mass and the carriage, firing the carriage downward one or more times and then lowering the mass so that the carriage may be removed through the access door.

PATENTEU AUB24I9YI SHEU 1 BY 3 VIII/{IIIIIIIIIIIIIII/ 11111111111 1 IN VEN TORS GiLBERT F. HiLL FREDERICK J.LOETTERLE BY FARRIS w. SMITH a,

STANLEY GRAY PATENIEUAUBMIHII .ymln WV sum 2 0r 3 INVENTORS. GILBERT F, HiLL FREDERICK J. LOETTERLE y FARRIS W.5M|TH z.

STANLEY GRAY BMW M g mag PNEUMATIC SHOCK TESTING MACHINE BACKGROUND OF THE INVENTION This invention relates to impact shock testing machines and more particularly to a pneumatically operated machine using air pressure for increased impact velocities.

Impact shock testing machines heretofore usually have been gravity operated, the specimens to be tested being mounted on a carriage which is mechanically raised to a predetermined height. When the lift device releases the carriage, it falls, guided in its descent, to a ground supported resilient pad or spring mechanism which give the impact the particular shock pulse which is desired, usually expressed in the form of a curve having a characteristic shape such as a sawtooth curve. Since the carriage carrying the specimens rebounds after it strikes the pad, some sort of a friction brake must be provided to prevent the carriage from falling again producing secondary shocks of decreasing intensity.

Pneumatic shock-testing machines have heretofore been known but these machines have usually been of the type for ordinance testing where the shock produced is that of acceleration not deceleration. The specimen'carrying carriage is locked in place by a latch mechanism and air under pressure is built up in a firing chamber. When the latch is released an acceleration shock is produced and the carriage is then decelerated by air pressure building up ahead of it in the tube in which it travels.

Testing requirements, particularly in the space industry, require impact shock testing of increasingly greater forces which would require a gravity operated machine of such height as to be impractical. Also, known impact testing machines have their pulse-producing pads ground-supported so that the shocks a produced are communicated to the ground or floor and thus interfere with other machines which may be nearby.

SUMMARY OF THE INVENTION The machine of the present invention is intended to subject test specimens to a high impact shock pulses. The carriage on which the test specimens are mounted is in the form of a piston which may be tired" downward by air pressure in a gunlike tube, which guides the carriage, against a pulse producing pad which is supported on a seismically supported reaction mass. A pneumatically operated latch mechanism retains the carriage in elevated position in the guide tube while air pressure is built up in the tube above the carriage. This air pressure may be varied for varying the velocity which the carriage attains at impact.

The reaction mass, at impact, is supported on a column of air in a base cylinder in which the mass moves like a piston. When air in the base cylinder below the mass is vented, the mass is lowered so that the carriage and specimens may be loaded or unloaded in the machine through a door at the landing stage which connects the base cylinder and the carriage guide or "gun" tube.

The pulse pad is carried on an anvil which, in turn, is supported on the mass, the anvil being capable of limited guided movement upward from the mass. The mass is annular and a reduced portion or stem of the anvil is slidingly contained in the central passage through the mass.

The comparatively large passage through the mass contains a smaller stop tube which is headed at its upper end to provide a stop to limit the upward movement of the mass when air is admitted under the mass through an electrically operated valve in the closed lower end of the base cylinder. The stop tube head is also in sealed engagement at all times with the central passage through the mass.

The lower end of the stop tube is secured in the closed lower end of the base cylinder and is provided with another valve controlled source of air which flows through the stop tube for lifting the anvil and pad against the lower open end of the carriage guide tube when the mass is elevated to its upper limit.

The anvil and pad are also annular, having aligned, small, central passages therethrough. After the carriage and attached specimens have been loaded through the access door and centered on top of the pad the mass is raised to introduce the carriage into the open lower end of the guide tube, air is introduced through the stop tube to lift the anvil and pad, the latter sealing against the lower end of the guide tube. Air from the stop tube then flows through the central passages through anvil and pad, which are smaller than the passage through the stop tube, to the guide tube, lifting the carriage beyond the latch.

The latch which has its own valve controlled source of air is then pneumatically operated to prevent passage of the carriage downward therepast and air through the stop tube is shut off allowing the carriage to descend to the latch. Thereafter, air under pressure is admitted through another electrically controlled valve to build up pressure above the latched carrier in the upper closed end of the guide tube.

When the predetermined pressure is reached the latch is disengaged and the a carrier is fired downward to strike the pad supported on the air-supported mass. As the carrier rebounds from the pad air is again introduced through the stop tub to again lift anvil and pad and to propel the carrier upward before it can fall and strike the pad again.

A programmer is provided to sequentially operate switches which control the various valves, the programmer being provided with counting means so that it may be set for one or more pneumatically propelled impacts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a prospective view of a machine according to the invention;

FIGS. 2 and 3 are enlarged, fragmentary, longitudinal sectional views of the lower and upper portions thereof, respectively;

FIG. 4 is a sectional view on the line 44 of FIG. 3;

FIG. 5 is a diagrammatical view of the machine of FIG. I including the air distribution system, a programmer and wiring diagram therefor;

FIG. 6 is a fragmentary, diagrammatical view of the lower portion of the machine with parts in position for loading or unloading;

FIG. 7 is a sectional view on the line 7-7 of FIG. 2; and

FIG. 8 is a perspective view of a programmer suitable for use with the machine of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the shock machine 10 has a baseplate 11 adapted to be bolted to the floor of the testroom. Secured to plate I], a cylinder I2, typically a steel tube, extends upward to a boxlike receiver or loading stage 13 having a hinged door 14. The receiver I3 has side of perforated metal, so that its interior is open to atmosphere and its upper plate is secured, as a by welding and/or clamp bolts, to an upper or guide tube I5, typically of steel tubing having an inside diameter somewhat less than that of the cylinder 12.

The top of tube 15, typically about 8 feet above the floor, is closed by a plug or breech block 16 and between the plug 16 and receiver 13, an annular latch mechanism I7 is secured.

Referring to FIG. 2, a plug l8 secured to plate 11 and cylinder 12, closes the lower end of the cylinder. An upwardly projecting tube 20 a has its bushed lower end secured by a setscrew 21 in a central well in plug 18, an air passage 22 leading the well. The bushing around the tube 20 is appropriately sealed so that air through passage 22 flows through the tube 20 and a resilient laminated annular pad 23 around the tube rests on the top of the plug 18. Another air passage 22:: extending up through the plug I8 is radially offset outward of pad 23.

The top of tube 20 is headed at 24 and another annular laminated pad 25 secured around the tube below its head 24 is in sealed engagement with the interior axial passage 26 through a heavy tubular steel body, herein called the mass 27,

which is slidable within cylinder 12. An annular stop ring 28 is bolted to the bottom of mass 27 and is appropriately sealed around tube so as to be slidable on the tube and to limit the upward movement of the mass 22 under pressure from air from passage 220, so that its upper end 29 may slide up into receiver 13 but stops short of the lower open end or nuzzle 30 of the upper or guide tube 15.

An annular anvil 31 has a reduced lower portion or stem 32 slidingly received in the passage 26 through the mass and appropriately sealed therearound. The lower end of stem 32 has a vertically elongated transverse hole or slot 33 therethrough, shown in FIG. 7, and a diametrically extending hole 34 through the mass contains a stop rod 35 through the slot 33 to limit the upward movement of anvil 31 with respect to the mass. Setscrews 36 in the hole 34 position the rod 35 in hole 34 across the stem in passage 26.

Anvil 31 normally carries an annular pulse producing pad 37 of resilient material such as bakelite," plastic or rubber. The pad is of slightly larger diameter than the end 30 of guide tube 15 and the upper edge of the pad and the lower end of the tube are bevelled so that when the pad is raised by the anvil against the tube, sealed contact results. Both anvil 31 and pad 37 have an axially extending passage 38 therethrough of a substantially smaller diameter than that of the passage through tube 20.

Anvil 31 is made in tow parts, an upper portion 310 and a lower portion 31b bearing the stem 32, the two parts being bolted together, as shown, so that a thinner portion 31b may be substituted if it is desired to use a thicker pad 37. The upper portion of the anvil 31 and the lower portion of the pad 37 carry an alignment tube 380 in the passages 38 therethrough for the alignment of the pad with the anvil.

Referring to FIG. 3 the upper plug 16 has air passages 39 and 40 adapted to receive pneumatic tube fittings for supplying and venting air in the guide tube.

The latch mechanism 17 comprises an upper ring 41 secured around the tube 15 by a plurality of setscrews 42. Below set screws 42 ring 41 surrounds the tube and the tube has six equiangularly spaced holes 43 through each of which a steel ball 45 may partially project inwardly, the holes being formed so that the ball will not completely pass through. Below ring 41 is another ring 46 bolted at a plurality of locations 47 a to ring 41 and the rings 41 and 46 have radially extending piston bores 48, best seen in FIG. 4, in which appropriately sealed pistons 49 are adapted to slide horizontally for forcing balls 45 into the holes in guide tube 15. An annular band 50 surrounds the rings 41 and 46 and an annular space or air passage 51 is left between the rings and band 50 communicating with each of the piston bores 48. A hole 52 adapted for connection with a pneumatic fitting is provided in ring 46 communicating with passage 51 for operation of the pistons 49.

Referring to P16. 5, the various air passages are connected to electrically operated pneumatic valves. A two-way, normally open vent valve A is connected to passage 39 in the upper plug 16 and a normally closed, two-way intake valve B is connected through a pressure regulating valve 53 to passage 40 a for admitting air under pressure to the upper end of tube 15 from an air pressure line 54 leading from the usual compressor 55, regulator valve 56, and filter 57.

Passage 51 in the latch 17 is connected at 52 to a three-way valve C which is connected to atmosphere and through a pressure regulating valve 58 to the air supply line 54.

At the base of the machine, the passage 22a to the cylinder 12 is connected through regulator valve 59 to a normally closed, two-way valve D which connects to line 54. Passage 22a is also connected directly to a normally open two-way valve E for venting cylinder 12.

Passage 22, leading to the tube 20, is connected through a pressure regulator valve 60 to a normally closed, two-way valve F also connected to line 54.

Referring again to P16. 3, a carriage 61 is shown in latched position and comprises a piston portion 62 and a fixture portion 63 bolted thereto. The piston portion 62 is of metal and has an outside diameter closely conforming to the inside diameter of guide tub 15 but freely slidable in the tube.

The fixture portion, it will be understood, is a block of any convenient shape having a plurality of recesses, not shown, in which test specimens such as transistors or the like can be inserted and locked into place by means well known in the art.

The bottom surface of the piston portion 62 has a cylindrical boss 62a projecting centrally down, the boss being adapted to fit into the central passage 38 of pad 37 above the tube 38a for aligning carriage 61 on top of pad 37 when loading, the mass 27 being lowered in cylinder 12, as shown in FIG. 6.

It will be apparent that a variety of programming means may be employed for timing the opening and closing of valves A-F, inclusive. Such a programmer 65 is shown diagrammatically in FIG. 8.

A motor 66 is mounted on a frame 67 adapted to drive, through appropriate gearing, a plurality of cams 68 on shaft 69 in the direction of arrow 70. A plurality of switches 71, mounted on frame 67, have an operating arm or cam follower 72 adapted to turn the switches on when the follower drops into a reduced perimetrical portion 73 of the cam, denoted 0-6 on one of the cams, and to turn the switch off when the follower rides up at 74 to the enlarged portion of the cam. A counter 75 may be attached to the end of shaft 69 opposite the motor.

Referring again to FIG. 5, a different switch 71 is connected, as shown in broken lines, to each of the valves A-F, inclusive, and switch 71G is connected through counter 75 to motor 66. A line L, of the electrical power source is connected to the motor 66, as shown, and to each of the valves A F by lines, not shown.

The other line L. of the source is connected, lines not shown, to each of the switches 71 through the switch 716 and is adapted to be connected by a pushbutton switch 76 to motor 66 and to one contact of a holding circuit relay 77, the other contact of which is connected through the switch 710, by lines not shown, to each of the other switches 71. The coil of relay 77 is connected to L, and, through switch 76, to L,.

The cam 68 which operates switch 710 is arranged to shut off the circuit to motor 66 and to the switches 71 at the end of a cycle when the relay 77 is no longer connected through counter 75.

Another pushbutton switch 78 is arranged, as shown by broken lines, to energize switches D and E when operated.

in operation the carrier 61 with specimens to be tested in fixture 63 is placed e centered on pad 37, which is in the position indicated in FIG. 6, and door 14 is closed. Preferably, the door is connected to a fail-safe switch connected in conventional manner to ensure that the cycle cannot start until the door is closed.

When the counter 75 is set for the number of cycles desired, valves A-F are all in their normal position. Pushbutton switch 78 is first manually activated to operate valves D and E and manually or it otherwise held depressed for about three seconds until the mass 27 rises in cylinder 12 with stop ring 28 against the stop pad 25 and carrier 61 is introduced into the guide tube 15.

Without releasing switch 78, switch 76 is then operated to start the motor 66 and to activate the switches 71 and the holding circuit at 77. The switches 71 are now in position not to activate switches A-C but to activate valves D, E, and F and pushbuttons 76 and 78 may be released.

Air passes through the passage 38 in anvil and pad to raise the carriage in tube 15 and after about 3 seconds, to give carriage 61 time to pass above latch 17, valve C to opens to lock the latch, valve F closes allowing the anvil and pad to drop and the anvil is again seated on the elevated mass. Simultaneously, valve A closes and valve B opens admitting a predetermined pressure charge into the pressure chamber in tube 15 above the carrier 61 which has dropped to seat on the balls 45 of the latch.

After an interval of about seven seconds, determined by the time necessary to build up the maximum amount of pressure which may be required through regulator 53, valve C closes and releases latch 17 by exhausting the pressure in passage 51 and carriage 6] is fired downward onto pad 37. During the passage of the carriage downward valve B is closed, discontinuing charging of the pressure chamber. Carriage 61 rebounds and, during the rebound, valve A is opened and the pressure chamber is vented.

At the same time valve F is opened again raising the anvil and introducing air under the carriage to prevent its falling again against the pad.

Assuming that the counter has been set for a number above one, air continues to lift the carrier again and the cycle is re peated.

When the counter reaches the number for which it is set, the switch HG closes valve F about one second after it was opened, by breaking the circuit to the other switches 7] allowing all valves to return to normal, including closing valve D and opening valve E exhausting air from the cylinder 12 and allowing mass 27 to call to the pad 23. The door can then be opened and the carrier and specimens removed.

A novel feature of this operation is the arrangement for the valve F to open again during the rebound of carriage 61 to introduce air under the carriage to prevent its striking the pad again before it is raised to the latched position. This is accomplished by a precise angular relationship between the cams of the switches 71 which operate the valves C and F. This angular relationship is determined by the pressure built up in the upper portion through the valve B and the height of the latch 17 above the pad 37 on the elevated mass 27 and valve F is opened during the approximately one-tenth second after carriage 61 reaches zero velocity on the pad and rebounds upward. Since air is admitted through valve F during their rebound period and carriage 6! is again carried upward, no friction brake or latch is required to prevent carriage 61 from striking the pad more than once after it is released from its latched position.

It will be apparent that a source of pressure other than compressor 55 may be used and other gases than air may be the fluid used. Under certain circumstances a negative pressure may be desirable in the tube [5 above the carriage 61 for firing it downward with less force and modifications to accomplish this will be obvious.

We claim:

l. in a pneumatically operated shock testing machine having a guide tube, a cylindrical specimen-carrying carrier slidable as a piston in the tube, latch means on the tube spaced from the normally closed upper end thereof and adapted to detain the carrier spaced from the tube open lower end, valve means for admitting pressured gas to the tube above the latched carrier and for venting gas therefrom, and means for operating the latch, the improvement comprising: a base, a cylinder projecting upward therefrom and having an open end spaced from and axially aligned with the tube bottom and thereby providing access to the tube for the carrier, a heavy tubular mass member mounted as a piston in the cylinder, a valve means connected to the cylinder for admitting pressured gas to raise the mass member in the cylinder and for venting gas therefrom, a stop tube projecting from the base and having a head in sealed relation with the e central passage of the mass member, an annular anvil carried 0 n the mass member and having a stern carried in the member passage and capable of limited movement therein as a cylinder, an annular pulse producing pad carried on the anvil, the top of the pad being substantially at the top of the cylinder when the member is lowered and the stop tube head being adapted to retain the member with the pad spaced form the tube when the member is raised, valve means for admitting pressured gas through the stop tube to the member passage to raise the anvil with the pad in sealing engagement with the tube, and programming means for operating the respective valve means and the latch-operating means, the valve means for raising the anvil and ad being programmed to operated at a timed interval after e carrier strikes the pad to prevent the carrier from falling back on the pad after rebounding and to raise the carrier again up to the latch means.

2. The testing machine defined in claim 1 having cycle programming means for the timed sequence operation of the valve means and latch operating means including a counter selectively adjustable for a plurality of cycle repetitions, the programming means, after the carriage has been placed upon the pad, first causing admission of gas to the cylinder for raising the mass member, then causing admission of gas to the mass member passage and venting the tube for raising the anvil and pad against the tube and introducing the carrier therein and thereafter raising the a carrier above the latch, then closing the latch an thereafter closing the vent means to the tube and allowing the carrier to sink to the latch, then causing admission of gas to the tube for building up pressure behind the latched carrier, then releasing the latch, then stopping the admission of gas to the tube and thereafter venting the tube and causing admission of gas again to the member passage for preventing fall back of the carrier and for repetition of the cycle, the counter being arranged to vent the cylinder and to stop the supply of gas to the member passage when the counter reaches the selected number of cycles for lowering the mass member and the carrier thereon for unloadmg.

3. A pneumatically operated shock testing machine having a vertically extending guide tube, a cylindrical specimen-carrying carrier adapted to slide as a free piston in the tube, and latch means on the tube adapted to secure the carrier in elevated position in the tube, the upper end of the tube being adapted to be charged with gas under pressure for firing the carrier downward when the latch is released, the lower end of the tube being adapted to receive and stop the carrier when it is tired downward, the lower end of the tube also having programming means for admitting gas under pressure thereto under the carrier when the carrier rebounds upward after being stopped at said lower tube end before the carrier can ball back again on the pad and for raising the carrier up to the latch means.

4. A pneumatically operated shock testing machine having a base, an upwardly projecting guide tube supported above the base and having a closed upper end, a cylindrical specimencarrying carrier slidable as a piston in the tube, latch means carried on the tube for securing the carrier elevated in the tube, a mass member supported on the base below the tube, a pulse producing pad carried on the mass member and adapted to be raised in sealed contact with the lower end of the tube valve means for admitting gas under pressure to the upper end of the tube for firing the carrier downward against the pad, means for releasing the latch, valve means for admitting gas under pressure to the lower end of the tube, the mass member and pad having connecting passages therethrough for conducting gas from said last mentioned valve means to the tube, and programming means for operating the valve and latch means for first admitting gas to the lower end of the tube to raise the carrier above the latch means, then to admit gas to the upper end of the tube and then to release the latch, the programming means then operating to admit gas again to the lower end of the tube after the carrier can fall back again on the pad.

gg gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,600,932 Dated August 24, 1971 Invent fl GILBERT F. HILL et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 5, for "as" read has column 2, line 54, for "side" read sides column 3, line 27, for "tow" read two--;

column 5, line 21, for "call" read fall 1-;

column 5, line 35, for "their" read this column 6, line 1, for "form" read from column 6, line 21, for "an" read and column 6, line 66, after "carrier" insert strikes the pad and rebounds and before the carrier strike the "a" in column 2, line 56; after "20" in column 2, line 64; column 3, line 60; column 4, line 57, strike the "11'; column 5, line 62 strike the e Signed and sealed this 1 4th day of March 1972.

Attest:

EDWARD ILFLEICHEH, JR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents 

1. In a pneumatically operated shock testing machine having a guide tube, a cylindrical specimen-carrying carrier slidable as a piston in the tube, latch means on the tube spaced from the normally closed upper end thereof and adapted to detain the carrier spaced from the tube open lower end, valve means for admitting pressured gas to the tube above the latched carrier and for venting gas therefrom, and means for operating the latch, the improvement comprising: a base, a cylinder projecting upward therefrom and having an open end spaced from and axially aligned with the tube bottom and thereby providing access to the tube for the carrier, a heavy tubular mass member mounted as a piston in the cylinder, a valve means connected to the cylinder for admitting pressured gas to raise the mass member in the cylinder and for venting gas therefrom, a stop tube projecting from the base and having a head in sealed relation with the e central passage of the mass member, an annular anvil carried o n the mass member and having a stem carried in the member passage and capable of limited movement therein as a cylinder, an annular pulse producing pad carried on the anvil, the top of the pad being substantially at the top of the cylinder when the member is lowered and the stop tube head being adapted to retain the member with the pad spaced form the tube when the member is raised, valve means for admitting pressured gas through the stop tube to the member passage to raise the anvil with the pad in sealing engagement with the tube, and programming means for operating the respective valve means and the latch-operating means, the valve means for raising the anvil and pad being programmed to operated at a timed interval after the carrier strikes the pad to prevent the carrier from falling back on the pad after rebounding and to raise the carrier again up to the latch means.
 2. The testing machine defined in claim 1 having cycle programming means for the timed sequence operation of the valve means and latch operating means including a counter selectively adjustable for a plurality of cycle repetitions, the programming means, after the carriage has been placed upon the pad, first causing admission of gas to the cylinder for raising the mass member, then causing admission of gas to the mass member passage and venting the tube for raising the anvil and pad against the tube and introducing the carrier therein and thereafter raising the a carrier above the latch, then closing the latch an thereafter Closing the vent means to the tube and allowing the carrier to sink to the latch, then causing admission of gas to the tube for building up pressure behind the latched carrier, then releasing the latch, then stopping the admission of gas to the tube and thereafter venting the tube and causing admission of gas again to the member passage for preventing fall back of the carrier and for repetition of the cycle, the counter being arranged to vent the cylinder and to stop the supply of gas to the member passage when the counter reaches the selected number of cycles for lowering the mass member and the carrier thereon for unloading.
 3. A pneumatically operated shock testing machine having a vertically extending guide tube, a cylindrical specimen-carrying carrier adapted to slide as a free piston in the tube, and latch means on the tube adapted to secure the carrier in elevated position in the tube, the upper end of the tube being adapted to be charged with gas under pressure for firing the carrier downward when the latch is released, the lower end of the tube being adapted to receive and stop the carrier when it is fired downward, the lower end of the tube also having programming means for admitting gas under pressure thereto under the carrier when the carrier rebounds upward after being stopped at said lower tube end before the carrier can ball back again on the pad and for raising the carrier up to the latch means.
 4. A pneumatically operated shock testing machine having a base, an upwardly projecting guide tube supported above the base and having a closed upper end, a cylindrical specimen-carrying carrier slidable as a piston in the tube, latch means carried on the tube for securing the carrier elevated in the tube, a mass member supported on the base below the tube, a pulse producing pad carried on the mass member and adapted to be raised in sealed contact with the lower end of the tube valve means for admitting gas under pressure to the upper end of the tube for firing the carrier downward against the pad, means for releasing the latch, valve means for admitting gas under pressure to the lower end of the tube, the mass member and pad having connecting passages therethrough for conducting gas from said last mentioned valve means to the tube, and programming means for operating the valve and latch means for first admitting gas to the lower end of the tube to raise the carrier above the latch means, then to admit gas to the upper end of the tube and then to release the latch, the programming means then operating to admit gas again to the lower end of the tube after the carrier can fall back again on the pad. 